By default, packed widgets resize if their container changes size - they don't scale themselves or their contents to the new size. This can lead to empty space between widgets, or cropped or cramped widgets if the user resizes the window.

One solution is to prevent resizing. We
bind
to the
<Configure>
event, which is sent when a widget's size or position changes, registering a callback to reset the window's size. This is how you'd ensure a popup error-message box couldn't be resized.

You often want to let the user resize the application's windows. You must then define how each widget will react. Do this through the arguments to the
pack
method:
-fill
controls the dimensions the widget will resize in, and
-expand
controls whether the widget's size will change to match available space. The
-expand
option takes a Boolean value, true or false. The
-fill
option takes a string indicating the dimensions the widget can claim space in:
"x"
,
"y"
,
"both"
, or
"none"
.

Different parts of your application will behave differently. The main area of a web browser, for example, should probably change size in both dimensions when the window is resized. You'd pack the widget like this:

$mainarea->pack( -fill => "both", -expand => 1);

The menubar above the main area, though, should expand horizontally but not vertically. You'd pack the widget thus:

$menubar->pack( -fill => "x", -expand => 1 );

Associated with resizing is the need to anchor a widget to part of its container. Here's how you'd anchor the menubar to the top left corner of its container when you call
pack
:

$menubar->pack (-fill => "x",
-expand => 1,
-anchor => "nw" );

Now when you resize it, the menubar stays at the top of the window where it belongs, instead of being centered in wide open space.